Data communications can limit the delivered performance of a system, such as a server. Typically, a processor, such as a micro-processor, communicates with other system components via electrical signals that exit the processor via pins on the processor package and/or socket. These pins are metal contacts that mate to metal contacts on the printed circuit board. Conductive paths on the printed circuit board, referred to as traces, route the signals from the mating metal contacts to other components or connectors on the printed circuit board. Connectors route the signals to other printed circuit boards and/or other system racks. Data communicated via these communication paths includes any bit transmitted over any distance, such as user data, application data, memory coherency traffic, and control signals.
Each communication path includes a pin and a driver circuit on the originating device. Each pin and driver circuit is part of an interconnect scheme, where the driver circuit is built to provide a signal that can be reliably received at a receiver. Typically, the interconnect scheme specifies the maximum trace length and the maximum number of connectors. For example, the interconnect scheme may specify a maximum trace length of 20 inches and a maximum number of connectors of 3 connectors.
The interconnect schemes have two limiting aspects, which are built into the driver circuit. First, the signaling rate or frequency is limited by signal integrity issues, where longer traces and more connectors reduce signal integrity. Second, more power is required to drive higher frequency signals over longer traces and through more connectors.
Often, at least some, if not most, of the power used by a driver circuit is lost and not received at the receiver. Instead, the power is lost in dissipated heat or lost in transit, due to such effects as resistive loss, reflection from impedance mismatches, and capacitive/inductive losses. Also, if the trace length is less than the maximum trace length and/or the number of connectors is less than the maximum number of connectors, the driver circuit wastes power by consuming excess power and providing excess power to the pin.
For these and other reasons there is a need for the present invention.